1. Field of the Invention
The invention relates to a magnetic recording and reproducing apparatus of a large capacity which is excellent in high-density recording and reproducing characteristics.
2. Related Background Art
In a magnetic recording and reproducing apparatus, in order to realize a miniaturization and a large capacity, there is a tendency at present to realize a high-density recording. In a field of a magnetic tape memory apparatus as well, in order to improve recording and reproducing characteristics in a high recording density region, various researches related to a magnetic tape and a magnetic head have been performed.
In a magnetic recording medium, in order to improve recording and reproducing resolutions in the high recording density region, it is necessary to increase a residual magnetization, realize a high coercive force to match the magnitude of the residual magnetization, and thin a magnetic layer. Particularly, from this viewpoint, as a medium that is superior to a conventional coated magnetic recording medium, a thin film magnetic recording medium made by a vacuum evaporating method, a sputtering method, an ion plating method, or the like attracts attention.
As a representative example of the thin film type magnetic recording medium, there is a metal evaporated tape which has been put into practical use for a VCR of the Hi8 system and a digital VCR of the DV format system. Different from a conventional longitudinal recording medium, the magnetic tape is characterized by having an oblique magnetic anisotropy such that an easy axis is inclined from a film normal direction of a magnetic layer. That is, the easy axis is not located in a film plane or in the film normal direction but the axis is located in the direction which is inclined from the film normal direction in a normal plane including the longitudinal direction of the tape. For example, in a commercially available metal evaporated tape for the Hi8 system VCR, the easy axis is inclined from the film normal direction by about 70.degree. in the normal plane including the longitudinal direction of the tape. A magnetization recorded by a ring type magnetic head is remained in the inclined easy axis direction, thereby forming a magnetization mode different from a conventional longitudinal recording. Due to the formation of such an inclined magnetization mode, the high recording density characteristics are remarkably improved as compared with that of the longitudinal record medium.
As it becomes clear that the above thin film tape is superior to the coated tape, which forms a longitudinal magnetization mode, it is being examined to introduce the thin film tape in a field of a VCR for broadcasting use and a magnetic tape storage device for computer in which hitherto, the coated tape such as an MP (metal particle) tape or the like has been a main stream as well.
In the VCR for broadcasting use and magnetic tape storage device for computer, what is called a separately recording and reproducing method in which a recording head and a reproducing head are individually provided is generally used.
Consequently, a signal just after completion of the recording is reproduced, thereby enabling a recording error to be reduced (called a read-after-write method). Moreover, a magnetic head parameter (or dimension) in a recording step and a magnetic head parameter (or dimension) in a reproducing step can be independently designed. That is, from a point to improve the recording and reproducing characteristics, the head parameters or dimensions having what is called a trade-off relation in a self recording and reproducing system are individually optimized in the recording and reproducing steps, so that excellent recording and reproducing performances can be obtained.
As an example of a design related to a gap length of each head, in the separately recording and reproducing system using the coated tape such as an MP tape or the like, a gap length of the reproducing head is designed so as to be properly small in correspondence to a recording signal band and a gap length of the recording head is designed so as to be larger than that of the reproducing head. The reason is as follows.
It is necessary to design the gap length of the reproducing head as small as possible in order to reduce a gap loss in a high linear recording density region. However, when the gap length of the recording head is miniaturized so as to be almost the same as that of the reproducing head, an enough recording magnetic field cannot be obtained and a tape magnetic layer cannot be saturation recorded, so that a problem such that a reproduction output is deteriorated, enough overwrite characteristics cannot be obtained, or the like occurs.
Particularly, the magnetic layer of the conventional coated tape is thicker than that of the thin film tape, so that it is difficult to completely record up to a deep layer of the magnetic layer.
In recent years, the MP tape in which a thickness of the magnetic layer is equal to several hundreds nm or less has also been developed due to the improvement in magnetic powder forming the magnetic layer. In this case, since it is necessary to provide a large recording magnetic field which can cope with a large coercive force of more than 170 kA/m, guidelines for designing of the head related to the foregoing gap length is fundamentally similar to the above.
From the above viewpoints, in the present magnetic recording and reproducing system having a linear recording density of flux reversals of about 100 kfrpi or less, there are many cases where, generally, the gap length of the reproducing head is set to about 0.20 .mu.m and the gap length of the recording head is set to 0.25 .mu.m or more.
As mentioned above, in the magnetic tape memory apparatus such as VCR for broadcasting use, magnetic tape storage device for computer, or the like using the separately recording and reproducing method, an optimum design to maximumly extract the magnetic recording and reproducing performances of the tape has been made.
In the magnetic tape memory apparatus of the separately recording and reproducing system as mentioned above, hitherto, since coated tape such as an MP tape or the like is used as a medium, the magnetic head parameters for recording and reproduction are optimized for the coated tape.
When the thin film magnetic tape is used for the separately recording and reproducing system, an excellent performance of the thin film type tape is not necessarily exhibited. For instance, in a system optimized for the MP tape, irrespective of using the thin film tape, a case where only an S/N ratio that is equivalent to that of the MP tape is obtained also occurs.
Up to the present, there has been hardly any example of a research and a development of the magnetic tape memory apparatus for separately recording and reproducing by using the thin film type tape. Thus, a construction of the separately recording and reproducing system suitable for the thin film tape is also unknown.
From the above technical background, at present, there is no magnetic recording and reproducing apparatus according to the separately recording and reproducing method, which can sufficiently make the most of excellent high recording density characteristics of a thin film tape.